Linking Nutrient Transport to Soil Physical Processes During Freeze/Thaw Events to Promote Wintertime Manure Management, Nutrient Use Efficiency, and Surface Water Quality

View the project final report

• 2015 annual report
• 2016 annual report

Commodities

• Agronomic: corn
• Animal Products: dairy

Practices

• Animal Production: manure management
• Crop Production: no-till, nutrient cycling
• Education and Training: demonstration, extension, workshop
• Production Systems: agroecosystems
• Soil Management: soil chemistry, soil physics, soil quality/health
• Sustainable Communities: sustainability measures

The application of dairy manure to the landscape during winter is a longstanding practice for farms in the Midwestern United States and other temperate regions. Practical motivations behind winter spreading include affordability, availability of time, and the reduced risk of compaction from farm equipment on frozen soils. Wintertime manure applications, however, coincide with environmental conditions that are prone to runoff and accelerate nutrient losses from agricultural fields. Understanding the nutrient dynamics in response to winter-applied manure is especially important to Wisconsin, a leading state in dairy production, where up to 75% of annual runoff volumes occur on frozen and thawing soils. The high potential for winter runoff, hence nutrient transport, has prompted revisions to winter manure regulations, yet little conclusive data exist to guide these changing standards.

Effective year-round management of dairy agroecosystems necessitates a mechanistic field evaluation of runoff generation and nutrient loading on land with winter-applied manure. Previous research investigated these systems, however, was historically confounded by observational study designs that could not account for the variability in winter weather patterns or the complexity of frozen soils. Moreover, field- and watershed-based manure management models have a limited capacity to simulate nutrient transport during winter because of the poor understanding of frozen agricultural conditions and the lack of empirical data to build appropriate routines. To expand the utility of frozen soil research to agriculture, however, advancements are needed to develop suitable instrumentation and field methodology. From this, the goals of this study are twofold. First, while measuring runoff nutrient losses from wintertime manure applications, practical management techniques are simultaneously evaluated to identify practices that minimize winter runoff. Specifically, the use of conventional fall tillage versus no-tillage is compared with the timing of winter manure applications: unmanured controls, early December applications to frozen ground (prior to snowfall), and late January applications to frozen, snow-covered soil. Second, to account for variability in weather, aid outreach, and improve the feasibility of applied agricultural research on frozen soils, a coupled water-energy balance is incorporated into the field design. Using intense field methods, this approach quantifies the underlying physical processes that drive runoff on frozen, agricultural soils, such as the rate of snowmelt and infiltration potential of frozen soils.

This field study is established in south-central Wisconsin at the University of Wisconsin Arlington Agricultural Research Station. A set of 18 plots (5 x 15 m each) are installed in a complete factorial arrangement (2 landscape tillage treatments x 3 manure timing treatments), in triplicate, and will be monitored for three winter seasons (2015-2016, 2016-2017, 2017-2018). The field contains a complete weather station, each plot is equipped with a runoff collection system, and a total of 125 automated sensors and 90 passive instruments have been installed to capture the water-energy balance. Data from the Winters of 2015 – 2016 and 2016-2017 have accounted for variability in weather patterns and are providing informative data on the effect of tillage, the timing of the manure applications, and the rate at which manure may be applied to a frozen soil. These findings will be supplemented with several smaller-scale laboratory collaborations that isolate the interactions between nutrient release from manure exposed to snowpack and the infiltration limits of variably-saturated frozen soils.

The overall goal of this study is to quantify nutrient losses in runoff from winter-applied liquid dairy manure and identify management practices that will optimize on-farm nutrient retention during winter. To accomplish this goal, hence overcome the previous and current challenges of agricultural field research during winter (i.e. variability in weather and complex frozen soil dynamics), the study design incorporates a coupled water-energy balance. Quantifying the drivers of winter runoff - the rate of snowmelt and infiltration potential of frozen soils - relative to manure and land management practices, both the variability in weather conditions and frozen soils properties may be integrated with runoff and nutrient load evaluations. This intense mechanistic field approach provides key insight into environmental processes during winter as well as establishes appropriate methodology for future research in frozen agricultural systems.

Within these goals, we define our performance targets as:

1) Establish a field site with 5-6% slope, characterize relevant properties of the site, and conduct a pilot study during the first winter season (winter 2014-2015) to test the proposed site design and instrumentation configurations. This pilot year is necessary because of the historic challenge in conducting agricultural field research during winter, the need to bridge theoretical knowledge of frozen soils with applied agriculture, and the importance of establishing effective methodology for frozen soil research.

2) After verifying the field design through a pilot season, install 18 large-scale plots (each 5 x 15 m) during the summer – fall 2015 (SARE Project Report 2016). These plots are planted with continuous corn for silage and assigned to conventional or no-tillage as well as one of three manure timing treatments: unmanured controls, early December applications to frozen ground (prior to snowfall), and late January applications to frozen, snow-covered soil.

3) Following the establishment of 18 field plots, equip each plot with individual runoff collection systems, soil temperature and moisture sensors, and instrumentation for soil frost and snow depth measurements. One plot per treatment (i.e. six plots) are equipped with additional instrumentation that bolster the water-energy balance: ground heat flux plates, infrared radiometers, and matric potential sensors. In addition to the comprehensive monitoring of the plots, establish a complete weather station to capture net radiation, wind speed, vapor pressure, air temperature, rain and snow-water equivalents, and snow depth. In total, this study design requires 125 automated sensors, and 90 passive instruments to be built, calibrated, and installed during summer – fall 2015.

4) Conduct the full-scale plot study for three winter seasons (2015-2016, 2016-2017, 2017-2018). During each of these three seasons, runoff and nutrient losses will be analyzed along with the water-energy balance parameters to partition nutrient losses from manure and tillage treatments as well as gain a process-level understanding of frozen soil and snow dynamics in response to manure applications. Outreach events will be hosted on the site for farmers, researchers, programmers, and government stake holders.

5) Analyze field data and build winter routines for manure management and biophysical models with collaborators. As data are combined with supplementary laboratory research, disseminate findings via peer-reviewed manuscripts, public outreach events, and local to national conferences.